The missing link?: Arabidopsis SPCH is a MAPK specificity factor that controls entry into the stomatal lineage

Mitogen activated protein kinase (MAPK) signaling modules that incorporate AtMPK3 and AtMPK6 control critical aspects of Arabidopsis biology including stress responses, development, cell division and cell death. Arabidopsis stomatal development is negatively regulated by the YDA-MKK4/5-MPK3/6 MAPK module and follows a three step pathway of asymmetric and symmetric divisions followed by terminal differentiation. We have identified the bHLH transcription factor SPCH, which controls entry into the stomatal lineage as a substrate of AtMPK3 and AtMPK6. These findings suggest that SPCH activity may be directly affected by environmental conditions to enable the plant to modify stomatal development in response to suboptimal climates.